Exemplary embodiments of the present invention relate to an integrated circuit, and more particularly, to an image sensor.
In general, an image sensor refers to a device which captures an image by using semiconductor properties that respond to light. A chare coupled device (CCD) image sensor has been widely used. However, as complementary metal oxide semiconductor (CMOS) technology has made rapid progress, an image sensor using CMOS has been developed. As compared to a conventional CCD image sensor, a CMOS image sensor has an advantage in that analog circuits including a pixel array and digital control circuits can be directly implemented on a single integrated circuit (IC).
An image sensor has as many comparators as the number of columns of a pixel array. Since the comparator is a circuit requisite to convert a pixel signal into a digital signal, it gives great influence on a quality of an output image. The comparator receives a ramp signal and a data signal, i.e., pixel signal related to an image provided from a pixel. The ramp signal gradually decreases at a constant rate. The comparator compares the data signal with the ramp signal to output a value to be stored as an image. Therefore, it is important to generate a reliable ramp signal from an internal ramp signal generation circuit so that an image sensor can store a reliable image.